Moving-body tracking device for radiation therapy, irradiation region determining device for radiation therapy, and radiation therapy device

ABSTRACT

A radiation therapy apparatus includes a radiation irradiation unit  35 , an X-ray imaging unit  36 , a CT imaging device  37 , a treatment planning device  38 , and a controller  10 . The controller  10  includes a CT image deformation amount calculation unit  11 , a shape calculation unit  12 , an irradiation region determining unit  13 , an X-ray image deformation amount calculation unit  14 , a position calculation unit  15 , a template matching unit  16 , a comparison unit  17 , a correction unit  18 , and an image processing unit  19 , and by comparing the positions of a treatment target locus in respective breathing phases and the positions of the treatment target locus in corresponding ones of the respective breathing phases identified by the template matching unit  16 , identifies the error values between the positions and the positions identified by the template matching unit  16  for each of parameters.

CROSS REFERENCE TO RELATED APPLICATIONS

This application relates to and claims §371 priority from SNPCT/JP2015/052967 filed Feb. 3, 2015, the entire contents of which areincorporated herein by reference, which in turn claims priority to JPSer. No. 2014-032888 filed Feb. 24, 2014.

FIGURE FOR PUBLICATION

FIG. 6

BACKGROUND OF THE INVENTION Field of the Invention Technical Field

The present invention relates to a moving body tracking device forradiation therapy and an irradiation region determining device forradiation therapy, and a radiation therapy apparatus thereof used for aradiation therapy that treats a patient by irradiating the patient witha treatment beam. Specifically, the moving body tracking device refersto a device that performs target tracking that tracks a target as amoving body moving along with patient's breathing or the like, andthereby tracks the position of the moving body.

Background Art

In radiation therapy that irradiates an affected area such as a tumorwith radiation such as an X-ray or an electron beam, it is necessary toaccurately irradiate the affected area with the radiation. However, theaffected area may move along with patient's breathing. For example, atumor near a lung largely moves on the basis of breathing. For thisreason, there is proposed a radiation therapy apparatus configured toarrange a metallic marker near a tumor, detect the position of themarker using an X-ray fluoroscope, and control the irradiation oftreatment radiation (see Patent Literature 1).

Further, in recent years, there has also been proposed markerlesstracking that can omit inserting a marker into the body of a patient by,instead of using a marker, performing the image recognition of theposition of a specific locus such as a tumor.

Still further, there is also proposed a method that prepares radiationtreatment planning using four-dimensional CT image data that contains agroup of three-dimensional images taken at different times (see PatentLiterature 2).

CITATION LIST Patent Literature

Patent Literature 1: Japanese Patent No. 3053389

Patent Literature 2: JP-2008-80131 A

ASPECTS AND SUMMARY OF THE INVENTION Technical Problem

In any of the case of the marker tracking that uses a metallic markerarranged inside the body of a patient as a target and the case of themarkerless tracking that utilizes a specific locus of a patient as atarget, in order to perform such target tracking, it is necessary torecognize the position of the target using image processing. Inaddition, the accuracy of the target tracking depends on settingparameters used when performing the target tracking. The appropriatevalues of the parameters depending on an individual patient are alsodifferent and therefore appropriately setting the parameters isextremely difficult and requires a lot of experience.

The present invention is made in order to solve the above problem, and afirst object thereof is to provide a moving body tracking device forradiation therapy and a radiation therapy apparatus that allow theparameters used when performing the target tracking to be easily set.

Also, in order to identify the position and shape of a treatment targetlocus, information on the position and shape of the treatment specificlocus in a preliminarily obtained reference breathing phase should becorrected in accordance with the body motion of a patient due topatient's breathing. Doing this work manually not only requires a lot ofworking hours but also causes an error.

The present invention is made in order to solve the above problem, and asecond object thereof is to provide an irradiation region determiningdevice for radiation therapy and a radiation therapy apparatus thatallow the position and shape of a treatment target locus, which aretaken along with the body motion of a patient, to be easily identified.

Solution to Problem

According to a first aspect of the present invention, a moving bodytracking device used for radiation therapy that treats a patient byirradiating the patient with a treatment beam comprises: an X-ray imageinformation acquisition unit that acquires a position of a treatmenttarget locus in a referential breathing phase and three-dimensionalX-ray image data consisting of a group of two-dimensional X-ray imagedata of a region, including the treatment target locus, in multiplesuccessive breathing phases from a storage device; an X-ray imagedeformation amount calculation unit that calculates a deformation amountof a two-dimensional X-ray image including the treatment target locusbetween different breathing phases by performing image registration onthe three-dimensional X-ray image data acquired from the storage device,and thereby; a position calculation unit that calculates positions ofthe treatment target locus in the respective breathing phases on thebasis of the position of the treatment target locus in the referentialbreathing phase acquired from the storage device and the deformationamount of the two-dimensional X-ray image including the treatment targetlocus between the different breathing phases calculated by the X-rayimage deformation amount calculation unit; a template matching unit thatacquires X-ray images of a region including the treatment target locusin the multiple successive breathing phases, prepares templates usedwhen performing tracking by setting parameters for template matching,and performs operations, identification of the positions of thetreatment target locus in the respective breathing phases, multipletimes changing the parameters; and a comparison unit that compares thepositions of the treatment target locus in the respective breathingphases calculated by the position calculation unit and the positions ofthe treatment target locus in the respective breathing phases identifiedby the template matching unit and identifies error values due to everyeach parameter or combination thereof.

According to a second aspect of the present invention, the parametersinclude the number of the templates acquired during one breathing cycleand/or a threshold value used for the template matching.

According to a third aspect of the present invention, a moving bodytracking device further comprises an image processing unit that displaysgraphically relationships between the number of the templates acquiredduring a breathing cycle and/or the threshold value used for thetemplate matching and the error values when changing the number of thetemplates acquired during a breathing cycle and/or the threshold valueused for the template matching.

A fourth aspect of the present invention is such that the imageprocessing unit graphically displays a two-dimensional color map thatrepresents the error values in different colors with the number of thetemplates acquired during a breathing cycle and the threshold value usedfor the template matching as a vertical axis and a horizontal axis,respectively on the display unit.

A fifth aspect of the present invention further comprises; a treatmentplanning storage unit that stores a shape of the treatment target locusin the referential breathing phase and four-dimensional CT image dataconsisting of a group of three-dimensional CT image data of the regionincluding the treatment target locus in the multiple successivebreathing phases; a CT image deformation amount calculation unit thatperforms image registration on the four-dimensional CT image dataacquired from the treatment planning storage unit, and therebycalculates a deformation amount of a three-dimensional CT imageincluding the treatment target locus between different breathing phases;a shape calculation unit that calculates shapes of the treatment targetlocus in the respective breathing phases on the basis of the shape ofthe treatment target locus in the reference breathing phase stored inthe treatment planning storage unit, and the deformation amount of thethree-dimensional CT image including the treatment target locus betweenthe different breathing phases calculated by the CT image deformationamount calculation unit; an irradiation region determining unit thatdetermines a treatment beam irradiation region on the basis of theshapes of the treatment target locus in the respective breathing phasescalculated by the shape calculation unit; and a treatment beamirradiation control unit that emits the treatment beam with use of thetreatment beam irradiation region determined by the irradiation regiondetermining unit and positions of the treatment target locus obtainedby, in the template matching unit, performing the template matching withuse of the parameters that have been corrected on the basis of the errorvalues identified by the comparison unit.

A sixth aspect of the present invention is a radiation therapy apparatusincluding the moving body tracking device for radiation therapyaccording to any of the first to fifth aspects of the present invention.

A seventh aspect of the present invention is an irradiation regiondetermining device for a treatment beam used for a radiation therapyapparatus that treats a patient by irradiating the patient with thetreatment beam, and comprises: a treatment planning acquisition unitadapted to, from a storage device, acquire a shape of a treatment targetlocus in a reference breathing phase and four-dimensional CT image dataconsisting of a group of pieces of three-dimensional CT image data of aregion including the treatment target locus in multiple successivebreathing phases; a CT image deformation amount calculation unit thatperforms the image registration on the four-dimensional CT image dataacquired from the storage device, and thereby calculates a deformationamount of a three-dimensional CT image including the treatment targetlocus between different breathing phases; a shape calculation unit thatcalculates shapes of the treatment target locus in the respectivebreathing phases on the basis of the shape of the treatment target locusin the referential breathing phase acquired from the storage device, andthe deformation amount of the three-dimensional CT image including thetreatment target locus between the different breathing phases calculatedby the CT image deformation amount calculation unit; and an irradiationregion determining unit that determines a treatment beam irradiationregion on the basis of the shapes of the treatment target locus in therespective breathing phases calculated by the shape calculation unit.

An eighth aspect of the present invention is a radiation therapyapparatus including the irradiation region determining device forradiation therapy according to the seventh aspect of the presentinvention.

Advantageous Effects of Invention

According to the first, second, third, and sixth aspects of the presentinvention, the parameters used when performing the target tracking canbe easily set with high accuracy.

According to the fourth aspect of the present invention, therelationships between the number of the templates acquired during theone breathing cycle and the threshold value used for the templatematching, and the error values between the positions of the treatmenttarget locus in the respective breathing phases calculated by theposition calculation unit and the positions of the treatment targetlocus in corresponding ones of the respective breathing phasesidentified by the template matching unit can be easily recognizedthrough the graphic display.

According to the fifth, seventh, and eighth aspects of the presentinvention, the positions and shapes of the treatment target locus, whichare taken along with the body motion of the patient, can be easilyidentified by using the image registration.

The above and other aspects, features and advantages of the presentinvention will become apparent from the following description read inconjunction with the accompanying drawings, in which like referencenumerals designate the same elements.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a radiation therapy apparatus accordingto the present invention.

FIG. 2 is a block diagram of the radiation therapy apparatus accordingto the present invention.

FIG. 3 is a flowchart illustrating the basis steps of radiation therapy.

FIG. 4 is a flowchart illustrating a target tracking preparation step.

FIG. 5 is an explanatory diagram illustrating an irradiation regionsynchronized with breathing.

FIG. 6 is an explanatory diagram illustrating a template matchingaction.

FIG. 7 is a schematic diagram of a two-dimensional color map graphicallydisplayed on a display unit 34.

FIG. 8 is a schematic diagram of the two-dimensional color mapgraphically displayed on the display unit 34.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made in detail to embodiments of the invention.Wherever possible, same or similar reference numerals are used in thedrawings and the description to refer to the same or like parts orsteps. The drawings are in simplified form and are not to precise scale.The word ‘couple’ and similar terms do not necessarily denote direct andimmediate connections, but also include connections through intermediateelements or devices. For purposes of convenience and clarity only,directional (up/down, etc.) or motional (forward/back, etc.) terms maybe used with respect to the drawings. These and similar directionalterms should not be construed to limit the scope in any manner.

It will also be understood that other embodiments may be utilizedwithout departing from the scope of the present invention, and that thedetailed description is not to be taken in a limiting sense, and thatelements may be differently positioned, or otherwise noted as in theappended claims without requirements of the written description beingrequired thereto.

Various operations may be described as multiple discrete operations inturn, in a manner that may be helpful in understanding embodiments ofthe present invention; however, the order of description should not beconstrued to imply that these operations are order dependent.

Embodiments of the present invention will hereinafter be described onthe basis of the drawings. FIG. 1 is a schematic diagram of a radiationtherapy apparatus according to the present invention, and FIG. 2 is ablock diagram illustrating the main control system of the radiationtherapy apparatus. Further, a radiation irradiation unit 35 and an X-rayimaging unit 36 constituting the radiation therapy apparatus areindependent devices and include controllers, respectively; however, FIG.2 illustrates the functional configuration of the whole of the radiationtherapy apparatus as the block diagram. Also, a configuration excludinga storage device 30, a radiation irradiation unit 35, a CT imagingdevice 37, and a treatment planning device 38 from the radiation therapyapparatus in FIG. 2 is the configuration of the moving body trackingdevice for radiation therapy or irradiation region determining devicefor radiation therapy according to the present invention.

The radiation therapy apparatus includes a treatment table 27 forplacing a patient 57. The treatment table 27 is capable of moving androtating in six-axis directions. Also, the radiation therapy apparatusincludes the radiation irradiation unit 35 having a horizontalirradiation port 21 and a vertical irradiation port 22, each of whichemits radiation such as an X-ray or an electron beam. Further, theradiation therapy apparatus includes the X-ray imaging unit 36 having: apair of X-ray tubes 25 and 26; and a pair of X-ray detectors 23 and 24for measuring X-rays that have been emitted from the X-ray tubes 25 and26 and passed through the patient 57. In addition, as each of the X-raydetectors 23 and 24, for example, an image intensifier (I. I.) or a flatpanel detector (FPD) is used.

Still further, the radiation therapy apparatus includes: the CT imagingdevice 37 that takes CT images of the patient 57; the treatment planningdevice 38 that prepares treatment planning for the patient 57; thestorage device 30 that is connected to an in-hospital system and thelike through a network to store various pieces of data of the patient57; an input unit 33 including a keyboard and a mouse; and a displayunit 34 including a liquid crystal display panel and the like. Inaddition, the whole of the radiation therapy apparatus is controlled bya controller 10.

The horizontal irradiation port 21 and the vertical irradiation port 22are fixed in an examination laboratory. Also, the X-ray detector 24 ismovable between an imaging position in front of the horizontalirradiation port 21 facing to the X-ray tube 26 through the patient 57and a withdrawn position spaced from the horizontal irradiation port 21,and the X-ray detector 23 is movable between an imaging position infront of the vertical irradiation port 22 facing to the X-ray tube 25through the patient 57 and a withdrawn position spaced from the verticalirradiation port 22.

The CT imaging device 37 takes three-dimensional CT images of thepatient 57 and provides the CT images including the affected area of thepatient 57 prior to performing radiation therapy. The CT images taken bythe CT imaging device 37 are sent to the treatment planning device 38,and the treatment planning is prepared on the basis of the pieces ofpatient data read from the storage device 30 and the three-dimensionalCT images taken by the CT imaging device 37 in the treatment planningdevice 38. In addition, the three-dimensional CT images of the patient57 are taken during at least one breathing cycle of the patient 57.Further, four-dimensional CT image data consisting of a group ofthree-dimensional CT image data of a region including a treatment targetlocus in multiple successive breathing phases is stored in a treatmentplanning storage unit 31 in the storage device 30 together with theshape of the treatment target locus in a reference breathing phase as apart of the treatment planning.

Also, when preparing the treatment planning, the acquisition of X-rayimages is performed on the patient 57 by the X-ray imaging unit 36(although it is possible to employ X-ray imaging or X-ray fluoroscopy,the following description is given on the assumption of employing theX-ray fluoroscopy). The X-ray fluoroscopy is performed on the patient 57during at least the one breathing cycle of the patient 57. In addition,three-dimensional X-ray image data consisting of a group oftwo-dimensional image data of the region including the treatment targetlocus in the multiple successive breathing phases is stored in an X-rayimage information storage unit 32 in the storage device 30 together withthe position of the treatment target locus in the benchmark referencebreathing phase.

The above-described controller 10 includes: a CT image deformationamount calculation unit 11 that calculates the deformation amount of athree-dimensional CT image including the treatment target locus betweendifferent breathing phases; a shape calculation unit 12 that calculatesthe shapes of the treatment target locus in the respective breathingphases; an irradiation region determining unit 13 that determines atreatment beam irradiation region; an X-ray image deformation amountcalculation unit 14 that calculates the deformation amount of atwo-dimensional X-ray image including the treatment target locus betweendifferent breathing phases; a position calculation unit 15 thatcalculates the positions of the treatment target locus in the respectivebreathing phases; a template matching unit 16 that identifies thepositions of the treatment target locus in the respective breathingphases by template matching; a comparison unit 17 that compares thepositions of the treatment target locus in the respective breathingphases calculated by the position calculation unit 15 and the positionsof the treatment target locus in corresponding ones of the respectivebreathing phases identified by the template matching unit 16 to identifythe error values therebetween; a correction unit 18 that correctsparameters on the basis of the error values; and image processing unit19 that graphically displays a two-dimensional color map, whichrepresents the error values in different colors, on the display unit 34.

Also, the controller 10 includes: a treatment planning acquisition unit41 that acquires the four-dimensional CT image data and the shape of thetreatment target locus in the benchmark reference breathing phase fromthe treatment planning storage unit 31; an X-ray image informationacquisition unit 42 adapted to acquire the three-dimensional X-ray imagedata and the position of the treatment target locus in the referencebreathing phase from the X-ray image information storage unit 32; and aradiation irradiation control unit 43 that controls the radiationirradiation unit 35 to emit the radiation as a treatment beam.

Next, steps of conducting a radiation therapy in accordance with whichthe radiation therapy is performed using the above-described radiationtherapy apparatus will be described. First, the basic steps of theradiation therapy will be described. FIG. 3 is a flowchart illustratingthe basic steps of the radiation therapy.

When performing the radiation therapy, after the patient 57 has enteredthe treatment room (Step S1), the patient 57 is positioned (Step S2).After the patient 57 has been positioned in a position appropriate forthe therapy, target tracking is prepared (Step S3). After that, theradiation irradiation unit 35 receives an instruction from the radiationirradiation control unit 43 to emit the radiation as the treatment beam(Step S4). Then, when a necessary treatment is finished, the patient 57is discharged from the treatment room (Step S5).

Next, the above-described target tracking preparation step (Step S3)will be described. FIG. 4 is a flowchart illustrating the targettracking preparation step. Further, the following description isregarding the case in which the treatment target locus is a tumor of thepatient 57.

When preparing the target tracking, the treatment beam irradiationregion is first set. At this time, the treatment planning acquisitionunit 41 in the controller 10 acquires treatment planning informationfrom the treatment planning storage unit 31 in the storage device 30(Step S31). The treatment planning information is recorded in RT-DICOM(Digital Imaging and Communication in Medicine). Also, from thetreatment planning information, the shape of the tumor to be treated andthe four-dimensional CT image data are acquired. Here, thefour-dimensional CT image data is data consisting of the group of thepieces of three-dimensional CT image data of the region including thetumor in the multiple successive breathing phases.

In addition, at this time, the data of the shape of an organ containingthe tumor can be acquired together, and the shape of the tumor and thelike can be superposed on CT data in the benchmark reference breathingphase, and the superposition is displayed, which can be checked by anoperator.

Subsequently, the CT image deformation amount calculation unit 11performs image registration on the four-dimensional CT image dataacquired from the treatment planning storage unit 31, and therebycalculates the deformation amount of a three-dimensional CT imageincluding the tumor between different breathing phases (Step S32). Morespecifically, nonlinear registration is performed on the CT image datain the respective breathing phases to thereby calculate the deformationamount (3D-Vector) of CT image data between the respective breathingphases.

Then, the shape calculation unit 12 calculates the shapes of the tumorin the respective breathing phases on the basis of the shape of thetumor in the referential breathing phase stored in the treatmentplanning storage unit 31 in the storage device 30 and the deformationamount of the three dimensional CT image including the tumor between thedifferent breathing phases calculated by the CT image deformationcalculation unit 11 (Step S33).

After that, the calculated shapes of the tumor are superposed on thethree-dimensional CT images in the respective breathing phases anddisplayed, and the operator checks a shape in each of the respectivebreathing phases to correct it as necessary (Step S34).

Subsequently, the irradiation region determining unit 13 prepares aregion that is based on the shapes of the treatment target locus in therespective breathing phases and added with a margin based on respiratorydisplacement to determine the breathing-synchronized irradiation regionof the treatment beam by the radiation irradiation unit 35 (Step S35).Irradiation with the treatment beam using the below-described templatematching is performed within the irradiation region.

FIG. 5 is an explanatory diagram illustrating the breathing-synchronizedirradiation region.

The shapes of the tumor in the respective breathing phases have beenalready calculated. A region obtained by adding a margin region 101based on the respiratory displacement to a gating window 100 that is aregion to be irradiated with the treatment beam around the positions 102of the tumor in the respective breathing phases is determined as thebreathing-synchronized irradiation region.

Then, parameters for preparing templates used for the target trackingare optimized to prepare the templates. At this time, the X-ray imageinformation acquisition unit 42 in the controller 10 acquires X-rayimage information from the X-ray image information storage unit 32 inthe storage device 30 (Step S36). In addition, the position of the tumorto be treated and the three-dimensional X-ray image data are acquiredfrom the X-ray image information. Further, the three-dimensional X-rayimage data is data consisting of the group of the two-dimensional X-rayimage data of the region including the tumor in the multiple successivebreathing phases.

Subsequently, the X-ray image deformation amount calculation unit 14calculate the deformation amount of a two-dimensional X-ray imageincluding the tumor between different breathing phases by performingimage registration on the three-dimensional X-ray image data acquiredfrom the X-ray image information storage unit 32 (Step S37). Morespecifically, the deformation amount (2D-Vector) of X-ray image databetween the respective breathing phases is calculated by performingnonlinear registration on the X-ray image data in the respectivebreathing phases.

Next, the position calculation unit 15 calculates the positions of thetumor in the respective breathing phases on the basis of the position ofthe tumor in the referential breathing phase stored in the X-ray imageinformation storage unit 32 and the deformation amount of thetwo-dimensional X-ray image including the tumor between the differentbreathing phases is calculated by the X-ray image deformation amountcalculation unit 14 (Step S38).

Then, the template matching unit 16 sets the initial values of theparameters for the template matching (Step S39). As such parameters inthe present embodiment, the number of templates acquired during the onebreathing cycle and the threshold value used for the template matchingare adopted.

Specifically, a parameter as to how many templates are prepared duringthe one breathing cycle of the patient 57 is employed as the firstparameter. As such templates, when performing marker tracking, imagesincluding a metallic marker are used, and when performing markerlesstracking, images including a specific locus (tumor) used in place of amarker are used. The target tracking is performed by performing thetemplate matching using the prepared multiple templates.

Also, as the second parameter, the threshold value used for the templatematching is employed. The threshold value refers to reliability used forthe template matching, in other words, when performing the templatematching, how the degree of matching between a template and the targetas the marker or the specific locus is required to recognize that thetemplate is the target.

Then, on the basis of the set parameters, the template matching unit 16acquires X-ray images of the region including the tumor as the treatmenttarget locus (the images are not particularly limited but in the presentembodiment, X-ray fluoroscopic images) to thereby prepare the templatesused when performing the tracking, as well as acquiring X-ray images ofthe region including the tumor in the multiple successive breathingphases (the images are not particularly limited, but in the presentembodiment, X-ray fluoroscopic images) (Step S40), and performs thetemplate matching on the successively acquired X-ray images using theprepared templates to thereby identify the positions of the treatmenttarget locus in the respective breathing phases (Step S41).

FIG. 6 is an explanatory diagram illustrating a template matchingoperation described above. In FIG. 6, the images used for the templatematching are denoted by a symbol M. Further, when performing themarkerless tracking using the specific locus such as the tumor, imagesof the specific locus such as the tumor are used as the images M. On theother hand, when performing the marker tracking using the marker, imagesof the metallic marker are used as the images M.

When preparing the templates respectively including the images M, bysuccessively fluoroscoping the patient 57, images 80 a, 80 b, 80 c, . .. , 80 n respectively including the images M are acquired. At this time,the images 80 a, 80 b, 80 c, . . . , 80 n respectively including theimages M are acquired by fluoroscoping the patient 57 during at leastthe one breathing cycle of the patient 57, for example, at a frame rateof approximately 30 fps (flames per second). Then, from the images 80 a,80 b, 80 c, . . . , 80 n respectively including the images M, image Mportions are extracted to obtain template images 81 a, 81 b, 81 c, . . ., 81 n. At this time, the images over which an image M moves areacquired with breathing of the patient 57. For this reason, asillustrated in FIG. 6, the acquired images M are sequentially deformed.

At this time, the number of the template images 81 a, 81 b, 81 c, . . ., 81 n prepared during the one breathing cycle is one of theabove-described parameters.

Subsequently, at the frame rate of approximately 30 fps, a regionincluding an image M is fluoroscoped. Then, the template matching isperformed on the region 83 including the image M in an image 82 acquiredat the regular intervals using the multiple template images 81 a, 81 b,81 c, . . . , 81 n. Specifically, all of the multiple template images 81a, 81 b, 81 c, . . . , 81 n are sequentially matched with the region 83including the image M in the image 82 acquired at the regular intervals.

When any of the multiple template images 81 a, 81 b, 81 c, . . . , 81 nexceeds the threshold value preset for the matching, it is determinedthat the matching is successful. Further, when some template imagesamong the multiple template images 81 a, 81 b, 81 c, . . . , 81 n exceedthe threshold value, a template image having the highest matching degreethereamong is recognized as a matched template image.

This time, the threshold value used for the template matching is one ofthe above-described parameters.

Referring to FIG. 4 again, the comparison unit 17 compares the positionsof the tumor in the respective breathing phases calculated by theposition calculation unit 15 and the positions of the treatment targetlocus in corresponding ones of the respective breathing phasesidentified by the template matching unit 16 to calculate error values(Step S42). Until all of preset parameter combination conditions arecompleted (Step S43), after the correction unit 18 has changed theabove-described two parameters (Step S4), the steps of Steps S41 to S43are repeated. Specifically, as the parameters, the number of templatesacquired during the one breathing cycle and the threshold value used forthe template matching are changed to prepare templates and the operationof performing the template matching on the X-ray images previouslysuccessively acquired by the fluoroscope using the templates is repeatedmultiple times with the use of the templates while changing theparameters so that error values for each of the parameters can becalculated.

On the other hand, when the error values between the positions of thetumor in the respective breathing phases calculated by the positioncalculation unit 15 and the positions of the treatment target locus inthe respective breathing phases identified by the template matching unit16 have been calculated for all combinations of the parameters (StepS43), the image processing unit 19 graphically displays thetwo-dimensional color map representing the error values in differentcolors on the display unit 34 (Step S45).

FIG. 7 and FIG. 8 are schematic diagrams of the two-dimensional colormap graphically displayed on the display unit 34. In addition, FIG. 7and FIG. 8 illustrate the two-dimensional color maps along mutuallyorthogonal directions (directions respectively corresponding to adetecting direction by the X-ray detector 23 and a detecting directionby the X-ray detector 24 in FIG. 1).

In each of the diagrams, the different colors are schematicallyrepresented by hatching patterns. Also, in each of the diagrams, thevertical axis represents the number of templates prepared during the onebreathing cycle of the patient 57, and the horizontal axis representsthe threshold value used for the template matching. Further, in a color(hatching pattern) band B in each of the diagrams, a region where theerror is larger is given upward. Still further, in each of the diagrams,the intersection area between mutually orthogonal straight linesdisplayed in the two-dimensional color map indicates a region where theerror is the smallest. These two straight lines are displayed on thebasis of arithmetic results by the comparison unit 17. Further, anoperator may designate the two straight lines.

By graphically displaying such a two-dimensional color map on thedisplay unit 34, the relationships between the number of the templatesacquired during the one breathing cycle and the threshold value used forthe template matching as the parameters, and the error values betweenthe positions of the treatment target locus in the respective breathingphases calculated by the position calculation unit 15 and the positionsof the treatment target locus in corresponding ones of the respectivebreathing phases identified by the template matching unit 16 can beeasily recognized.

The above-described steps complete the target tracking preparation step(Step S3) including the treatment beam irradiation region setting, theparameter optimization, and the template preparation. Theabove-described treatment beam irradiation (Step S4) is performed usingthe treatment beam irradiation region and the templates based on theoptimized parameters obtained in the target tracking preparation step.

Further, without limitation to the above-described embodiment,modification is also possible as follows. Specifically, until the errorvalues between the positions of the tumor in the respective breathingphases calculated by the position calculation unit 15 and the positionsof the treatment target locus in corresponding ones of the respectivebreathing phases identified by the template matching unit 16 fall withinan allowable range, after the correction unit 18 has changed theabove-described two parameters, S41 to S43 are repeated. When the errorvalues between the positions of the tumor in the respective breathingphases calculated by the position calculation unit 15 and the positionsof the treatment target locus in corresponding ones of the respectivebreathing phases identified by the template matching unit 16 fall withinthe allowable range, the parameters are automatically determined.

REFERENCE SIGNS LIST

-   10 Controller-   11 CT image deformation amount calculation unit-   12 Shape calculation unit-   13 Irradiation region determining unit-   14 X-ray image deformation amount calculation unit-   15 Position calculation unit-   16 Template matching unit-   17 Comparison unit-   18 Correction unit-   19 Image processing unit-   21 Horizontal irradiation port-   22 Vertical irradiation port-   23 X-ray detector-   24 X-ray detector-   25 X-ray tube-   26 X-ray tube-   27 Treatment table-   31 Treatment planning storage unit-   32 X-ray image information storage unit-   34 Display unit-   35 Radiation irradiation unit-   36 X-ray imaging unit-   37 CT imaging device-   38 Treatment planning device-   41 Treatment planning acquisition unit-   42 X-ray image information acquisition unit-   43 Radiation irradiation control unit-   57 Patient-   80 a to 80 n Images acquired by fluoroscopy-   81 a to 81 n Template images-   82 Image acquired by fluoroscopy-   83 Region including image M-   100 Gating window-   101 Margin region based on respiratory displacement-   102 Positions of tumor in respective breathing phases

Having described at least one of the preferred embodiments of thepresent invention with reference to the accompanying drawings, it willbe apparent to those skills that the invention is not limited to thoseprecise embodiments, and that various modifications and variations canbe made in the presently disclosed system without departing from thescope or spirit of the invention. Thus, it is intended that the presentdisclosure cover modifications and variations of this disclosureprovided they come within the scope of the appended claims and theirequivalents.

1.-6. (canceled)
 7. An irradiation region determining device forradiation therapy, wherein the irradiation region determining device fora treatment beam is used for a radiation therapy apparatus that treats apatient by irradiating the patient with the treatment beam, comprising:a treatment planning acquisition circuit that acquires a shape of atreatment target locus in a reference breathing phase andfour-dimensional CT image data consisting of a group of pieces ofthree-dimensional CT image data of a region including the treatmenttarget locus in multiple successive breathing phases from a storagedevice; a CT image deformation amount calculation circuit that performsimage registration on the four-dimensional CT image data acquired fromthe storage device, and thereby calculate a deformation amount of athree-dimensional CT image including the treatment target locus betweendifferent breathing phases; a shape calculation circuit that calculatesshapes of the treatment target locus in the respective breathing phaseson a basis of the shape of the treatment target locus in the referencebreathing phase, the shape being acquired from the storage device, andthe deformation amount of the three-dimensional CT image including thetreatment target locus between the different breathing phases, thedeformation amount being calculated by the CT image deformation amountcalculation circuit; and an irradiation region determining circuit thatdetermines a treatment beam irradiation region on a basis of the shapesof the treatment target locus in the respective breathing phases, theshapes being calculated by the shape calculation circuit.
 8. Theirradiation region determining device, according to claim 7, furthercomprising: a radiation therapy apparatus that generates said treatmentbeam.